Unidirectional broadband light emission from supported plasmonic nanowires

Metal nanowires are thought to become key elements in future nanophotonics applications. Here we show that single crystal silver nanowires supported on a dielectric interface behave similar to broadband unidirectional antennas for visible light. The degree of directionality can be controlled through the nanowire radius and its dielectric environment and the effect can be interpreted in terms of so-called leakage radiation from surface plasmons propagating in a single direction along a wire. We measure a forward-to-backward emission ratio exceeding 15 dB and an angular spread of 4° for wires with radii of the order 150 nm on glass in air. These findings could pave the way for development of metal nanowires as subwavelength directors of light in solar, sensor, and spectroscopy applications.